My car is freezing up please see details below.

I have a Mitubishi Magna Sedan 1995 V6, I was driving along and without no notice (no lights on dashboard or temperature gauges changing) my car decelerated to the point I was foot to the floor going aroung 40kmph. So I pulled over turned the car off, started car back up and no matter what gear I was in it didn't budge my car had locked up. 1 hour later I could drive it normally. Then surely enough it happened again. What is going on? I cannot find anything online to help me, I also took it to a mechanic and they couldn't see the problem.